Piston



Dec. 18, 1928. 1,695,417

J. 5.. DIAMOND PISTON Original Filed May 18. 1922 Patented Dec. 18, 1928.

UNITED STATES PATENT OFFICE.

JAMES EDWARDS DIAMOND, OF MOUNT VERNON, NEW YORK, ASSIGNOR TO THE CLEVELAND TRUST COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF 0310.

PISTON.

lppllcation filed May 18, 1922, Serial No. 561,997. Renewed September 14, 1927.-

radially in com ination and simultaneously,"

and is adapted to have a snug sliding fit in the cylinder so that upon the expansion of the piston either locally or generally due to the temperature conditions Within the engine, the provisions made will eliminate the possibility of the-piston seizing or scoring in the cylinder, even with the cylinder in a lcomaratively cold state, and after the cylinder has acquired its normal operating temperature with consequent expansion, the piston Will tend to occup the same general relation with thecylin er existing originally.

The invention also consists of the constructions which will be hereafter described in detail and particularly pointed out in the appended claims.

struction of the general principles shown in the earlier Franquist Patent, No. 1,153,9 O2. The specific construction ofthe present 1n-- vention leiids itself to inuch better manufacence to the metal cores, which as is well known, must' be subdivided into a number of parts so as to be collapsible for'ready removal from the interior of a structure of the shape of a piston, that is, ones with internally projectin bosses, ribs, etc.

In t e accompanying drawing Fig. 1 shows a View in perspective of a piston constructed in accordance with the principles of my invention. Fig. 2 a front elevation half. in section, and Fig. 3 an end elevation half in section, Fig. 4 an end view looking into the piston and Fig. 5 a detail showing a specific construction.

Referring to the drawings, the pistons shown may be regarded as consisting of two parts, a head 1 and a skirt 2, the head being considered that part carrying the piston rings and as far down as the actual sliding or glidin'g surface. For reasons well known to en- This is another detail con-- ture in metal molds particularly with refergine builders, it is necessary to depend upon the skirt of the piston to prevent the slap of I the piston within the cylinder, and heretofore it has been necessary to allow considerable free play between the piston skirt and the cylinder to take care of the expansion of the piston before the cylinder walls become. heated and to insure against any of the troubles previously mentioned. After the engine has been running for a comparatively after the cylinder has expanded due to its becoming warmed up.

In order to insure quiet operation it is proposed to use a piston having a skirt that shall be partially or entirely relieved from the undesirable mechanical expansion-when this existsproduced by the thermal expansion of the highly heated piston head due to the high temperature of combustion and that shall be automatically yielding in a circum ferential direction, radially, or 'both circumferentially and radially, as need be, to meet the conditions existing in an engine. One embodiment of such a construction is shown in the drawings and will now be described.

Projecting inwardly frointhe inner surface of the skirt are ribs or webs; These ribs may extend the entire inside length of the piston, may terminate directly back of the circumferential grooves or slots (3) or may be any length dictated either by the general design of the piston, such as the location of the Wrist pin or by shop production considerations. In the cases where a web construction is not used, it is necessary to cast in or machine the slot or slots or groove or grooves, which while joining the circumferential slot may or may not extend to the bottom of the skirt, it being permissible in some cases to have "the bottom of the skirt an unbroken circle. When the slots or grooves (4) are cast in the piston or I in the boss carrying sections, the walls of the grooves preferably diverge outwardly, as is clearly shown in Fig. 5.

will be no piston Circumferential slots or grooves (3-3) are cut into the outer surface of the piston separating the skirt portion of the piston either partially or entirely from the head in so far v may be machined in, is usually essential, but

its exact proportions such as depth and extent must be determined for each case. Its circumferential extent is dependent upon a number of variants, but it is my usual practice to carry this relief from the zone of the piston pin bosses well beyond the longitudinal slots (4:) starting with a maximum depth of relief directly coincident with an element passing thru the wristpin axis and gradually decreasing to nothing at a' point beyond the longitudinal slots (4). Among the reasons for this relief is that it provides space to accommodate the mechanical expansion of the boss-carrying portions of the skirt produced by the thermal expansion of the head anjda flexure of this portion of the piston due to the deflection of the wrist pin under load.

I locate the maximum depth of relief on the boss carrying sections, as just described, partly because I believe that the greatest amount of actual outward movement-of these sections is along a longitudinal line passing thru the wrist pin axis. Progressively decreasing clearance is provided from this line of maximum clearance beyond the slots (4) and toward the center of bearing sections 7 of the skirt, the outside diameter across which is the maximum diameter of the piston skirt. Naturally the circumferential length of the reliefs andthe depth thereof vary with different pistons and must always be suflicient to permit the piston to function under oper- "ating conditions in an engine without undue friction, scoring or seizing.

In machining a piston of this character, the skirt is given a relatively snug sliding fit within the cylinder, so that even when starting up with the engine and piston cold there slap,.'and due to the minimum clearance used oil pumping is largely if not entirely eliminated. Due to the high temperature of the explosive gases the piston as a whole will commence to expand with the first explosions, the head of the piston, howhotter, will exthan the skirt which is maintainedconsider- :ably cooler than the head by reason of dissipation of much of the heat o'ffthe head before it reaches the skirt. I n the construction in which the piston head and skirt are peripherally integral, the thermal expansion of the head is usually sufliciently great to expand ormove outwardly mechanically the boss carrying portions of the skirt. These boss carrying portions tend, due to their position and the forces created by the expansion of the head, in my construction of the ribs or webs (5), automatically to draw the floating sections either circumferentially around the walls of the cylinder or to flatten the arc of these sections, thus tending to withdraw these partially independent sections of the skirt from contact with the cylinder wall, moving the elements in the diametral plane normal to the wrist pin axis in a radially inward direction, in effect flattening these'circular portions of the skirt and making such transverse diameter become the axis of some form of ellipse.

T he construction also provides for the ac ditions, and offers an automatic compensating feature.

The ribs 8-, as shown inFig. 3, are each integral with a boss 9 boss carrying wall-6, the ring flange 10 and end wall 11.

In addition to all these marked advantages any tendency toward radially outward expansion due to operation conditions, of the portions of the skirt in contact with the cylinder wall (neglecting the oil film), namely, all but the relieved portions of the surface of the partially independent sections of the piston when cold, and preferably the entire surface of saidsections when under nor.- mal operating conditions is provided for in the constructions-suggested, the ribs or webs 5 being rigid enough to car the load due to the impulse force and ro angularity at the same'time having suflicient give automatically to compensate for the excess expansion, this being takenup by the gfiooves in webs5.

. The construction is compensating with respect to normal and'excess expansion in at least the several ways shown. The expansion of the piston skirt will thereforebe held within proper bounds and the piston will operate within the cylinder without seizure or scoring, yet at the same time maintaining a snug sliding fit, which will prevent piston slap, and will, due to such snug sliding fit, tend to keep the oil from working past the piston skirt and beyond the. head. After the engine has been running a comparatively long period of time the water in the jacket becomes heated and the cylinder expands,

but any free play which would otherwise oceure will be automatically Compensated for by a tendency of the skirt portions of the piston to resume, relatively, their normal positions.

Another advantage of a'skirt of this character is that ample rovision is made to take care of distortion 0 the cylinder from a true circle in cross section, such cylinder distortion being more or less common with internal combustion engines, and with a skirt that is substantially, radially and circumferentially compressible throughout, a considerable portion of, or for the entire skirt length any distortion of the cylinder will cause one or more sections of the piston toyield and obviate the likelihood of seizure.

While I have shown a particular embodiment'of the earlier Franquist invention in constructing a piston which'is adapted to yield circumferentially, radially or both simultaneously due to mechanical expansion conditions set u within the piston by the heat encountere in operation as well as beyielding due to contracting with the cyl- 1n im ler wall when expanding and; lending itself very well to casting-in dies, etc., yet it is the intention to cover broadly a piston having askirt which has been freed entirely or in part from the mechanical expansion produced by the thermal expansion of the piston head, and which skirt is circumferentially, radially or simultaneously circumferentially and radially yielding. to the flexure exerted by the cylinder walls when the skirt portion is expanded, and that due to the utilization of the mechanical expansion of the portions of the skirt integral with the head, an automatic compensatory element in the expansion andengine, having a head, a skirt and iston in bosses on the skirt, said head and s irt beingparti'ally separated by a circumferential slot and said skirt being further provided with vertical slots leading from the' circumferential slot and extending into the piston pin bosses and forming a groove therein. 3. A piston for an internal combustion engine comprising a head and a skirt,the skirt having oppositely disposed, exteriorly relieved, boss carrying sections connected to the head and provided withlongitudinal slots having outwardly diverging walls, and oppositely disposed bearing sections separated from the head by circumferential slots and united tothe boss carrying sections.

In testimony whereof Ihereunto aflix my signature this 21st day of February, 1925.

JAMES E. DIAMOND. 

